The invention relates to a processing liquid spreading device, particular saving electric power consumed thereby.
A camera or a printer using mono-sheet type instant film unit, or non-peeling apart type self-developing film unit (hereinafter referred to as simply film unit) have a processing liquid spreading device for spreading a processing liquid over a photosensitive layer of the unit while transporting the film unit out of the camera or the printer after exposure of the film unit. After being exposed, the film unit is picked in the trailing end and moved to a bite of a pair of pressure-applying rollers of the processing liquid spreading device by well-known picking device having a claw, then discharged out of the camera or the printer by the rotating pair of pressure-applying rollers while spreading the processing liquid. The pair of pressure-applying rollers and the picking device are driven by a common electric motor via a plurality of gears and cams.
The film unit comprises a rupturable pod containing a processing liquid in the leading end portion and a trap member to catch an excess processing liquid after being spread by the pair of pressure-applying rollers. Thus a thickness of film unit changes along its moving direction. Consequently, the load applied to the motor increases, which requires a larger torque when the thicker portions of the film unit such as the rupturable pod portion or the trap member portion pass through a bite of the pair of pressure-applying rollers in addition to starting to rotate the motor. A conventional instant camera or printer using the film unit has to have a battery and a motor capable of generating a large power, capacity and torque to cope with the increase of load.
The battery having a large power and capacity also requires larger size, which causes a size of the camera or printer to increase and makes them inconvenient to carry and handle. On the contrary, using a smaller size battery decreases the maximum number of pictures to be taken and influence the quality of pictures because of insufficient ability to spread the processing liquid.
Japanese Laid-open Patent 232639/90 (tokkai-hei 02-232639) shows the technology to solve the problem above mentioned, which includes a capacitor charged by multiplying the voltage of the battery and a switching control circuit to generate a switching signal at the time a load applied to a pair of pressure-applying rollers increases to supply power from the capacitor to the motor to increase its torque. However, such technology needs an additional capacitor, multiplying voltage circuit and switching control circuit, which increase the cost of the camera. Moreover, the motor also needs the ability to cope with high voltage supplied from the capacitor, which also increases the cost. Furthermore, it is not so effective in terms of overall power saving of battery, even though it is effective in terms of decreasing a peak current the battery has to supply.
An object of the invention is to provide a processing liquid spreading device for an instant film unit which can save the power of a battery without increasing the cost.
Another object of the invention is to provide a camera or a printer using the film unit capable of taking more pictures without using a large capacity battery which leads to a larger size camera or printer.
In the invention, a processing liquid spreading device for instant film unit comprises a pair of processing liquid spreading rollers; a motor for driving the pair of processing liquid spreading rollers; and a reduction gear to transmit a rotation of an output shaft of the motor to the pair of processing liquid spreading rollers while reducing a rotational speed of an output shaft of the reduction gear, wherein a reduction ratio of the reduction gear varies in sequence as the film unit advances so that a load fluctuation applied to the motor can be reduced. The reduction gear includes a driven gear which rotates one turn or less to complete a transportation cycle of the film unit and a driving gear to transmit the rotation of an output shaft of the motor to the driven gear. As the driving gear, an irregular formed gear is used and the driving gear is movable and biased in a direction toward a rotational axis of the driven gear to mesh therewith.
The irregular formed gear has a configuration that a distance between a periphery and a rotational axis thereof varies corresponding to a thickness variation in the film unit in the advancing direction. For example, the irregular formed gear has a first sector portion and a second sector portion corresponding respectively to a leading end portion and trailing end portion of the film unit, the first sector portion includes the largest distance between the periphery and the rotational axis and the second sector portion includes the second largest distance.
In some embodiments, the driving gear is moved along a direction toward the rotational axis of the driven gear by a cam integrally rotating with the driven gear so that the driving gear can be meshed therewith. As the cam, a cam slot is used which is formed on a side of gear which rotates integrally with the driven gear. Another type of the cam is a cam plate which rotates integrally with the driven gear and the driving gear is biased by using a sun and planet gear mechanism in a direction toward a rotational axis of the driven gear to mesh therewith.
A sun and planet gear mechanism can be used instead of biasing spring to keep the driving gear meshed with the driven gear. A worm wheel and worm can be used as the reduction gear.